The present invention relates to novel organosilicone polymers and their use in the manufacture of urethane cellular products, particularly flame-retarded flexible polyether polyol-based urethane foams.
It is well known that the urethane linkages of urethane foams are formed by the exothermic reaction of a polyfunctional isocyanate and a polyfunctional active hydrogen-containing compound in the presence of a catalyst, and that the cellular structure of the foam is provided by gas evolution and expansion during the urethane-forming reaction. In accordance with the "one-shot process" which is the most widely used industrial technique, direct reaction is effected between all of the raw materials which include the polyisocyanate, the active hydrogen-containing compound, the catalyst system, blowing agent and surfactant. A major function of the surfactant is to stabilize the urethane foam, that is, prevent collapse of the foam until the foamed product has developed sufficient gel strength to become self-supporting.
It is also well known that suitable active hydrogen-containing compounds include polyether polyols and polyester polyols. From the standpoint of their chemical structure, therefore, urethanes are usually classified as polyether and polyester urethanes, respectively. Urethane foams also differ with respect to their physical structure and, from this standpoint, are generally classified as flexible, semi-flexible or rigid foams.
Although certain techniques of urethane manufacture such as the "one-shot process" and certain components of the foam formulation such as the polyisocyanates, amine catalyst and blowing agent, are generally useful, a specific problem associated with the production of a particular type of urethane foam and the solution thereto are often peculiar to the chemical and physical structure of the desired foamed product. In particular, the efficacy of the foam stabilizer is usually selective with respect to the formation of a particular type of foam. One factor to be considered in the evaluation of stabilizing efficacy is surfactant potency which is reflected by two types of measurements. One is the measured original height to which the foam rises as it is being formed. From this standpoint, the greater the foam rise, the more potent is the surfactant. The second potency measurement is concerned with the ability of the surfactant to maintain the original height of the foam once it has formed. Foams produced with surfactants which have good potency in this second respect undergo a minimum of settling or "top collapse" which may otherwise contribute to split formation and other foam defects.
It is also desirable that the foam stabilizer have good processing latitude, that is, ability to provide foams of satisfactory quality over a relatively wide range of operating variables such as, for example, concentration of surfactant and metal co-catalysts which are normally employed in the manufacture of flexible polyether-based foams. The more common co-catalysts are organic derivatives of tin and thus sensitivity to variation in co-catalyst concentration is more particularly referred to in the art as "tin operating latitude." Decreasing the concentration of such co-catalysts below normal levels is sometimes necessary to improve breathability of the foam but, if the effectiveness of the foam stabilizer is narrowly dependent on co-catalyst concentration (that is, its tin operating latitude is poor), the desired enhanced breathability will be offset by foam weakness due to split formation.
The search for improved surfactants for stabilization of polyurethane foams is further complicated by the tendency of such foams to ignite readily and burn and the need to reduce their flammability. This characteristic is particularly objectionable in the case of flexible polyurethane foams in view of the use of such foams in many applications where fire is especially hazardous such as their use in automotive seat cushions and household furniture cushioning. One approach to reducing flammability of flexible foams is to include a flame-retarding agent such as various phosphorus and/or halogen-containing compounds as a component of the foam-producing reaction mixture. It is found, however, that surfactants which may otherwise be effective stabilizers of non flame-retarded foams, may be deficient as stabilizers of flame-retarded foams.
Among the various types of surfactants which have been used to advantage for stabilization of non flame-retarded flexible polyether-based urethane foams are polyoxyalkylene-polysiloxane block copolymers wherein silicon of the siloxane backbone is bonded only to methyl groups and the polyether portion of the polyoxyalkylene blocks is composed of oxyethylene and oxypropylene units. Such copolymers include those of both the hydrolyzable and non hydrolyzable types, that is, copolymers in which the polysiloxane and polyoxyalkylene blocks are linked through --Si--O--C-- and --Si--C-- bonds, respectively. From the standpoint of possessing a particularly good combination of potency and processing latitude in the stabilization of flexible polyether urethane foams, an especially useful class of non hydrolyzable block copolymers are those described in U.S. Pat. No. 3,505,377, an application for reissue of which was filed on Nov. 18, 1971 as Ser. No. 200,242 of Edward L. Morehouse, now U.S. Pat. No. Re-27,541. When used to stabilize polyether-based foams derived from reaction mixtures containing a flame-retardant, however, copolymers wherein the polysiloxane blocks are substituted only with methyl groups including copolymers of the hydrolyzable type, provide foams which either do not qualify as self-extinguishing (by flammability test ASTM D-1692-68) or do not provide self-extinguishing foams of low burning extent.
The prior art also describes polysiloxane-polyoxyalkylene block copolymers wherein the backbone of the polysiloxane blocks are modified with various groups other than or in addition to methyl groups, such as aralkyl groups. Copolymers of this type are described in U.S. Pat. No. 3,657,305 and in copending application Ser. No. 888,067, filed Dec. 24, 1969, of Edward L. Morehouse, now U.S. Pat No. 3,686,254. Although such copolymers, and especially those containing phenylethyl groups bonded to silicon, provide flame-retarded foams of significantly reduced flammability, it has been found that such foams have a tendency to settle leaving room for still further improved organosilicone foam stabilizers.
It is an object of this invention to provide new and useful organosilicone polymers which have particular application in the manufacture of flexible polyether polyol-based polyurethane foams.
Another object is to provide an improved class of polysiloxane-polyoxyalkylene block copolymers which possess a good combination of properties such as potency and processing latitude when used as stabilizers of flexible polyether urethane foams and which additionally allow for the formation of self-extinguishing foams of low burning extent and good quality with minimum sacrifice in their aforementioned other desirable properties.
A further object is to provide particularly flexible polyether polyurethane foams of reduced flammability and a method for their manufacture.
Various other objects and advantages of this invention will become apparent to those skilled in the art from the accompanying description and disclosure.